UAV-assisted wireless communications have been widely used to enhance network coverage as well as network performance [1]}, [2]}, [3]}. In [1]}, [2]}, the authors used the UAV for providing the network for the disaster relief missions. A UAV can also serve as an energy source provider for device-to-device communications [3]}.
Recently, RIS technology has been introduced as a low-cost and easily installed technology to mitigate interference and direct transmitted signals toward their receivers [7]}, [8]}, [9]}, [10]}. In [8]}, the authors considered two-way communications assisted by a RIS. The reciprocal channel to maximize the signal-to-interference-plus-noise ratios (SINR) and the non-reciprocal channel with the target of maximization of the minimum SINR was considered. The gamma approximation was used for the reciprocal channel, while the semidefinite programming relaxation and a greedy-iterative method were used for the non-reciprocal channel. In [9]}, an iterative algorithm with low computation complexity was proposed to solve the joint optimization of transmit beamforming vector and the phase shift of a RIS under proper and improper Gaussian signalling. In [10]}, the authors optimized the beamforming matrices at the BS and the reflective vector at the RIS to minimize the total transmit power at a multiple-input-single-output (MISO) non-orthogonal multiple access (NOMA) networks. An algorithm based on the second-order cone programming-alternating direction method of multipliers was proposed to reach an optimal local problem.
